Various processes have been developed for altering the physical properties of a fabric by applying various agents to the fabric, usually during a finishing process. For example, it is well-known to impart durable wrinkle resistance to cellulose fiber-containing fabrics such as cotton by impregnation of a continuous length of fabric with an aqueous solution of a suitable low molecular weight thermosetting resinous precondensate or cellulose crosslinking agent of a small enough molecular size to penetrate the cellulose fiber structure, usually with an appropriate catalyst, and eventual curing of the impregnated fabric. Such treatments have been effective in improving the shape-holding properties of cotton fabrics and have resulted in a greatly increased demand for durable press cotton fabrics because these combine the traditional comfort, washability and economy of the native fibers with the easy care properties desired in today's textile market. To facilitate garment manufacture, the cure of such resin-treated fabrics is delayed until after the treated fabric is cut and sewn to produce the desired finished garment and after such garment is given the desired shape by pressing.
A particularly promising approach to the production of easy-care, durable press garments has involved the wet fixation of resin- or polymer- forming creaseproofing agents, such as formaldehyde-melamine precondensates, as disclosed, for example, in U.S. Pat. No. 3,138,802. In this type of process, fiber system such as a cotton fabric is protected against excessive strength loss and presensitized for durable press processing by fixation of a suitable polymer-former and creaseproofing agent within the fibers while they are wet and swollen but without greatly altering the dry crease recovery angle or durable properties of the fiber system. The latter properties are only imparted in the desired degree during a subsequent dry cure. Such a process accordingly permits ready creasing or other distinct shaping of the fiber system during apparel manufacture or the like subsequent to the wet fixation step and prior to the delayed dry cure. However, wet fixation processes heretofore known have usually required neutralization and wash-off of the strongly acid wet fixation catalyst subsequent to the wet fixing step, to be followed by drying and then recatalyzation and redrying prior to the actual cure, thus requiring additional processing time and effort.
Other promising approaches to the production of easy-care, durable press garments have involved exposing a condition cotton fabric to formaldehyde and gaseous sulfur dioxide and heating the fabric under controlled moisture conditions, as disclosed, for example, in U.S. Pat. No. 3,706,526, and in copending application Ser. No. 237,056 of Swidler et al, filed Mar. 22, 1972, assigned to the assignee of the present application. These processes result directly in a cured fabric.
A superior durable press process is disclosed in U.S. Pat. No. 3,642,428. This process includes applying to a cellulose fiber-containing fabric a solution containing a polymer former such as a melamine-formaldehyde or urea-formaldehyde precondensate and a latent curing catalyst. Subsequently, the fabric while in a water swollen state is exposed at an elevated temperature in the presence of formaldehyde to a gas which is a strong acid (e.g., acetic acid, formic acid, hydrogen chloride) or capable of forming a strong acid by reaction with formaldehyde (as in the case of sulfur dioxide). The resulting fabric, which now contains the polymer former wet fixed therein, is dried to form a fabric which contains the wet fixed resin. This dry fabric may then be sewn to form a garment which may have creases hot pressed into it and the garment may finally be cured in the presence of a latent curing catalyst to impart durable press properties to it. As an alternative, the fabric containing the wet fixed resin and latent catalyst may be cured and thus have durable press properties imparted to it before it is made into a final product such as bed linen, if desired, a garment.
Treatment of the fabric with formaldehyde and sulfur dioxide must be carried out under carefully controlled conditions of temperature and humidity in order to achieve optimum results as the crosslinking reaction based on formaldehyde and sulfur dioxide is self-limiting in that removal of water from the system causes decomposition of the strong sulfonic acid which serves as a catalyst for this reaction. Another important consideration in a process of this type is providing suitable apparatus which prevents leakage of hazardous or noxious reactants, such as formaldehyde and sulfur dioxide, out of the apparatus. Both formaldehyde and sulfur dioxide are noxious and pungent, and leakage of these materials into the atmosphere around the processing apparatus is objectionable from the point of view of safety or industrial hygiene.
Various processes are also known to impart flame retardancy to cellulosic fiber-containing fabrics. For example, the fabric may be padded with a suitable flame retardant precursor compound and then contacted with ammonia gas to deposit on the fabric a polymerized phosphorus-containing material. Ammonia gas, however, is highly toxic and forms an explosive mixture with air at moderate concentrations of ammonia. Leakage of ammonia into the atmosphere around the processing apparatus is therefore objectionable and dangerous.